The invention concerns adjustable resistors in hybrid circuits.
In hybrid circuits technology, adjustable film resistors the resistance of which must be adjusted to a given value with a preset precision, for example of 10.sup.-3, consist of a main element in series with additional elements which are originally short-circuited by conductors. Adjustment consists in selecting the short circuits to be cancelled. Measuring the value of the resistance of the main element will determine which conductors must be cut for the purpose of increasing the resistance to its rated value. It is known to adjust the resistance during the measurement by means of a focused electromagnetic radiation serving to cut the conductors, as indicated in French Pat. No. 2,018,251, which was filed on May 29, 1970, by Siemens. According to this patent, the radiation may emanate from a laser, from an incandescent lamp or from a gas discharge. There exist automatic machines which measure the resistance of the main element of each resistor to be adjusted, which calculate from the result of said measurement the position of the short circuits to be cut off and which control the relative position of the resistor and of the beam in order that the latter may successively open the short circuits which are to be opened. Such machines are very costly and it is important to reduce the duration of the operation on each resistor so as to ensure a maximum working rate.
The object of the present invention is to provide a film resistor made of a resistive layer deposited on an insulating support consisting of a main element and short-circuited additional elements whose resistances are so chosen as to necessitate on average a minimum number of cuts of the short-circuiting conductors during the adjustment of a batch of resistors of like rated value and given precision.